Friday, September 14, 2012

How Preposterous News Propagates

Every so often – perhaps more frequently, if you're continuously canvassing the literature – there's a rapturous press release regarding a new medical innovation that seems too good to be true.  And, you wonder, how does the lay media get it so wrong?

This study reviewed a consecutive convenience sample of published literature, looking for articles resulting in press releases.  Then, they looked for elements of the article that made it into the press release, as well as the relative accuracy of the release compared with the overall findings of the article.  Essentially, what they found is that press releases were most likely to have "spin" if the conclusion of the article abstract misrepresented the study findings with "spin".

The authors also have an interesting summary of the sort of "spin" found in abstracts that misrepresent study findings.  These include:

 • No acknowledgment of nonstatistically significant primary outcome
 • Claiming equivalence when results failed to demonstrate a statistically significant difference
 • Focus on positive secondary outcome
 • Nonstatistically significant outcome reported as if they were significant

...and several others.

"Misrepresentation of Randomized Controlled Trials in Press Releases and News Coverage: A Cohort Study"

Wednesday, September 12, 2012

When Positive D-Dimers are Negative

This is the latest article from Jeff Kline, published in Thrombosis and Haemostasis (don't you all subscribe to that, too?), concerning pulmonary embolism and d-Dimer.

Wouldn't it be great if the d-Dimer wasn't a dichotomous cut-off?  Where, if a patient were of sufficiently low pre-test probability, a d-Dimer value that was nearly negative still contributed adequately to a negative likelihood ratio to reduce the probability of a significant pulmonary embolism?  Well, that's the theory behind this article – which looks at d-Dimer measurements combined with age, Wells' score, and Revised Geneva scores.

There are a lot of complex tables in this article breaking down the various potential cut-off values for d-Dimer along with different pre-test probabilities, and the concept presented is that potentially higher cut-off values of d-Dimer can be used without missing PEs larger than sub-segmental.  This is presented in context that a higher cut-off might allow reductions in imaging, which seems fair.

However, the most interesting thing in this article to me is Figure 3 – which is d-Dimer concentration compared with fractional obstruction of pulmonary vascular tree.  It is, unfortunately, pretty clear there's not a great linear relationship between dimer and pulmonary obstruction.  Most low d-Dimers had < 5% obstruction of the vascular tree, but at least one patient with a "negative" d-Dimer had 20% obstruction.  Beyond that, patients were just as likely to have 90% obstruction with modestly elevated d-Dimers than with massively elevated d-Dimers.

"D-dimer threshold increase with pretest probability unlikely for pulmonary embolism to decrease unnecessary computerized tomographic pulmonary angiography"
www.ncbi.nlm.nih.gov/pubmed/22284935

Monday, September 10, 2012

Not-So Routine Surgery on Dabigatran

This correspondence, published in Blood in March, was probably pretty easy to overlook.


A patient enrolled in RE-LY, the trial comparing dabigatran and warfarin for non-valvular atrial fibrillation, underwent open aortic valve replacement surgery.  As instructed, he discontinued his dabigatran two days prior to the surgery.

Had a little bit of a bleeding problem.

After 26 units of RBCs, 5 packs of platelets, 22 units of FFP, 5 x 10 units of cryoprecipitate, two doses of protamine, two doses of tranexamic acid, and five doses of Factor VIIa, the patient was finally stable enough to be evacuated to the ICU for dialysis to remove the remaining dabigatran.

What's most fabulously ironic about this correspondence is that the authors use this horrifying case to sprightly conclude Factor VIIa and hemodialysis are viable and effective reversal strategies for dabigatran-associated bleeding.

The patient – "The postoperative course was complicated by prolonged ventilation/Enterobacter pneumonia, asymptomatic nonocclusive femoral DVT (by surveillance ultrasonography [postoperative day (POD 7)]), and acute-on-chronic renal failure. Discharge to a rehabilitation facility occurred on POD56." – probably disagrees.

Would you be surprised if I mentioned there's a COI issue involving the authors and the manufacturer?

"Recombinant factor VIIa (rFVIIa) and hemodialysis to manage massive dabigatran-associated postcardiac surgery bleeding"
www.ncbi.nlm.nih.gov/pubmed/22383791